R_HOME path getting munged in inst/doc/Makefile on Windows

Hello,

I have come across two separate packages that have a Makefile in inst/doc
which use the R_HOME variable.

In both cases, the path to R_HOME gets munged in such a way that commands
that include R_HOME fail on Windows:

For example, one Makefile, for the xmapcore package (
https://hedgehog.fhcrc.org/bioconductor/trunk/madman/Rpacks/xmapcore/username/password:
readonly) has this:

R=${R_HOME}/bin/R
SUITE=../cookbook/delia.R
[...]
${R} --vanilla --verbose < ${SUITE}

the output of trying to build this package includes:

* creating vignettes ... ERROR
E:\biocbld\BBS-2~1.8-B\R/bin/R --vanilla --verbose < ../cookbook/delia.R
E:biocbldBBS-2~1.8-BR/bin/R: not found
make: *** [pdf] Error 127
Error in tools::buildVignettes(dir = ".") : running 'make' failed
Execution halted

It seems R_HOME is not getting resolved to a valid path. That's strange
because R CMD echo shows the right thing:

E:\sandbox>\biocbld\bbs-2.8-bioc\R\bin\R CMD echo %R_HOME%
e:/biocbld/bbs-2.8-bioc/R

That's a nice path with all forward slashes and no funny 8.3 paths with
tildes.  But it looks like when R_HOME is invoked in a Makefile, the
resulting path has a mix of forward and backslashes, and gets translated
into 8.3 style, and the resulting path is not valid for finding R
executables.

Note that R_HOME is defined within R; I don't also have it defined at the
shell level:

E:\sandbox>echo %R_HOME%
%R_HOME%

Any ideas?
Thanks,
Dan

sessionInfo()

R version 2.13.0 alpha (2011-03-18 r54865)
Platform: i386-pc-mingw32/i386 (32-bit)

locale:
[1] LC_COLLATE=English_United States.1252
[2] LC_CTYPE=English_United States.1252
[3] LC_MONETARY=English_United States.1252
[4] LC_NUMERIC=C
[5] LC_TIME=English_United States.1252

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

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